The Influence of External Conditions 37 



The Influence o] Light, Electricity, Centrifugal Force, Chemical 

 Substances, and Oxygen on the Caterpillars and Pupce of 

 Moths and Butterflies 



It has been shown by Grafin von Linden that the size, the 

 colors, and the markings of butterflies may be altered by sub- 

 jecting the caterpillars or the pupae to several kinds of external 

 conditions other than temperature. In general, however, the 

 results are similar to the effects produced by higher and lower 

 temperatures. 



Light. Vanessa urticae and V. io were used. Some of 

 the caterpillars were kept, with their food, in red, or green, or 

 blue light. Others were kept in the dark. The principal 

 changes were in the ground color of the wings of the butterflies. 

 This was intensest and brightest in red light, dusky in green, 

 and paler in blue and in the dark. The butterflies of V. urticae 

 were largest from the caterpillars reared in the blue, and of V. 

 io in the dark. The changes in the markings were very slight. 



Electric Shocks. The pupae of V. urticae, in a fresh but dry 

 condition, were put into an iron box through which an electric 

 current was passed of sufficient strength to cause a pricking 

 sensation when applied to the hand. In other cases one elec- 

 trode was applied at the wing axis arid the other at the tip of 

 the wing case. The resulting butterflies were brightly colored. 

 The black border of the wing was broader, and the tip of the 

 wing was sometimes dark. The blue and yellow scales of the 

 sides of the wing were little developed. 



Centrifuge. After the pupae had become hard they were 

 subjected to a centrifugal force for ten minutes each day. The 

 effects were in general similar to those caused by light. 



Chemical Substances. Contrary to the results of Standfuss, 

 who found changes in the food had no influence on the color 

 of the moth r except'in one case, when salt was added to the food 

 of Callema, Grafin von Linden found that certain substances 

 given with the food produced distinct effects. Some effects, for 

 the most part slight, were obtained with (i) defibrinated blood; 



